1. Field of the Invention
This invention relates to an improved ink jet printing apparatus and method for generating ink drops on demand under control of suitable electrical signals.
2. Description of the Prior Art
There have been known in the prior art ink jet printing systems in which a transducer is selectively energized to produce ink drops on demand. The prior art drop-on-demand printing systems have been generally limited by a low drop production rate, low resolution and low efficiency.
Commonly assigned U.S. Pat. No. 4,266,232 discloses apparatus for drop-on-demand ink jet printing in which the transducer is driven with voltage control pulses at a selectively controlled amplitude at a synchronous rate. This apparatus produced ink drops of equal size and spacing at an improved print rate and with improved print quality.
Copending application Ser. No. 274,989, filed June 6, 1981, by Lee et al entitled "Drop-On-Demand Method and Apparatus Using Converging Nozzles and High Viscosity Fluids" discloses a further improved system which is capable of operating with high viscosity ink to produce high resolution printing at still higher drop rates. However, under some operating conditions, the system failed to properly start after a period of rest or idling. In these cases, the first few drops after idle time (during which no drops were ejected) were either not ejected at all or were ejected with diminished velocity and/or uncontrolled direction so that the first few characters after idling exhibit missing or misplaced drops.